1. Field of the Invention
The present invention relates to a yellow fluorescent substance and a light-emitting device using the same. The present invention also relates to an illumination device comprising the light-emitting device and a vehicle comprising the illumination device.
2. Description of the Related Art
Recently, a white light-emitting device in which a semiconductor light-emitting element is used in combination with a fluorescent substance has been developed. The semiconductor light-emitting element emits light from a near-ultraviolet range to a blue range. An example of the semiconductor light-emitting element is a light-emitting diode. The semiconductor light-emitting element may be used as an exciting light source for the fluorescent substance. Such a white light-emitting device has a long life and uses much less power.
In one example of such a white light-emitting device, a blue light-emitting diode is used in combination with a yellow fluorescent substance. In the example, a part of the light emitted from the blue light-emitting diode is converted into yellow light using the yellow fluorescent substance. The remaining blue light emitted from the blue light-emitting diode is mixed with the yellow light which has been provided through the yellow fluorescent substance to give white light. In another example of the white light-emitting device, a light-emitting diode selected from the group consisting of a near-ultraviolet light-emitting diode, a violet light-emitting diode, and a blue-violet light-emitting diode is used in combination with the blue fluorescent substance and the yellow fluorescent substance. In such a white light-emitting device, at least a part of the light emitted from the light-emitting diodes is converted by the blue fluorescent substance and the yellow fluorescent substance. The light which has been thus converted is mixed to give white light.
White light-emitting devices are used for light sources of various illumination devices. From a viewpoint of an improvement of design, a vehicle illumination device in which a light source thereof has been downsized is expected to be provided.
United States Pre-Grant Patent Application Publication No. 2009/0050846 discloses a phosphor from the class of the oxynitride silicates represented by a chemical formula M1-kSi2O2N2:Eu2+k(M=Ca, Sr, or Ba). This phosphor from the class of the oxynitride silicates is one of typical yellow fluorescent substances excited by light having a wavelength from a near-ultraviolet range to a blue range.